Education
He graduated from the Leicester City youth academy.
He graduated from the Leicester City youth academy.
He has represented England at under-17 level. Leicester City
He continued to feature for Leicester's academy and reserves side for the next season before being promoted to the first team squad in July 2008 making regular appearances in their pre-season games. On 29 August 2008, just a few days after his 17th birthday, O'Neill signed a three-year professional contract, tying him to Leicester until the summer of 2011.
O'Neill's next first team involvement for Leicester came almost a year later when he was named as an unused substitute in their opening day fixture against Swansea City. He made his first appearance of the season three days later, playing the full 90 minutes as Leicester beat Macclesfield Town 2–0 in the League Cup. On 26 December 2009, O'Neill made his League debut for Leicester, coming on as a half-time substitute against Sheffield United, replacing the injured Jack Hobbs.
On 18 February 2010, O'Neill joined Tranmere Rovers on a one-month loan. On 31 January 2011, he joined Conference Premier team Kettering Town on a one-month loan. Mansfield Town
On 30 June 2011, O'Neill signed for Conference Premier side Mansfield Town, arriving on a free transfer.
O'Neill helped Mansfield to a play-off semi final where they lost 2–1 on aggregate to York City. His performances throughout the season attracted Championship clubs Burnley, Cardiff City and Ipswich Town. Burnley had a bid rejected by the Conference club, but manager Paul Cox admitted O'Neill could leave if the offer is right.
Burnley
On 15 June 2012, O'Neill signed for Championship club Burnley for an undisclosed fee. He signed for League Two club York City on a 28-day emergency loan on 4 October 2013. His debut came the following day in a 3–0 away defeat to Torquay United, before scoring his first goal for York in a 2–2 draw away at Chesterfield with a 30 yard shot into the bottom right corner.
On 31 October 2013, O'Neill's loan was extended until 4 January 2014, after making six appearances and scoring one goal for York. He had made 16 appearances and scored one goal for York. On 17 January 2014, O'Neill signed for League Two side Southend United on a 30-day emergency loan.
He joined Scunthorpe United on a three-month loan on 18 August 2014 and made his debut a day later in a 2–0 home defeat to Fleetwood Town. On 26 February 2015 he joined Leyton Orient on loan until the end of the 2014–15 season. Southend United
O'Neill rejoined Southend United, by this time in League One, on a one-month loan on 22 August 2015.
He had his Burnley contract terminated by mutual consent on 1 September 2015, ahead of a permanent transfer to Southend on a two-year contract.